Electric light bulb



o. s. LEVI EI'AL 2,405,261 ELECTRIQ LIGHT BULB Aug. s, 1946.

Filed Dec. 2,- 1944 w E L. m M

T. d H. M9 H. i H

Patented Aug. 6, 1946 ELECTRIC LIGHT BULB Application December 2, 1944, Serial No. 567,796

8 Claims. (Cl. 176-16) 1 This application is a continuation in part of applicants prior application Serial No. 432,168, filed February 25, 1942.

' This invention relates to an electric light, and

more particularly to a bulb for an electric lamp with a filament of tungsten or the like, with a coating on .the bulb which modifies the emitted light in a desirable manner.

Specifically, the preferred form of the invention comprises a bulb modified so that it accentuates the light rays in the range of from about -'500 millimicrons to 560 millimicrons in wave :as to accentuate the green range of the rays, is much more restful on the eye than the unmodified light. Specifically, the invention provides a modification of the light which increases the relative quantity of the rays, in the range specified above, by about 20% over the average as emitted by the filament and reduces glare and results in a visibility exceeding that of the unmodified light from either a clear or ordinary inside frosted bulb with a like filament energized by the same amount of current. The result is not nly a very efficient light but also a light which tires the eye much less than one Where there is a greater percentage of less effective light rays.

- The invention also relates to a specific manner of constructing the light bulb so as to obtain the desired result. One specific form of the invention will be described first and then modifications'will be suggested.

In the accompanying drawing forming a part of'this' specification, there is shown in Figure 1 a light bulb of typical form. In Figure 2 there is 1 shown an enlarged cross-section of a portion of the bulb.

The bulb comprises the usual base I!) with a filament ll indicated in dotted lines and supported from the base, and with a glass bulb l2 enclosing the filament. The bulb comprises the usual glass Wall l3, indicated in Figure 2 as be- -ing provided on the inside with a frosted surface i l4 for dispersing the light. The outside of the glass bulb is covered with a substantially transparent enamel I5 in which there is a light sprinkling of a highly reflective pigment Hi. The pigment may be composed largely of chrome green.

It will be seen that the light emitted from the filament ll will be dispersed by the frosting l4 and pass outward through glass I3 and the en- -amel 15. A certain portion of the light will encounter the sides of particles of the pigment l6 and be reflected in such a direction that it will pass on outward through the enamel. A consider- STATES 'PATET yros able portion of the light which strikes the pigment is reflected back into the bulb and across the bulb to the other side where it will again encounter dispersion and a certain amount of reflection. With a highly reflective pigment the reflection back and forth across the bulb will be repeated many times before all of the light is emitted. Each reflection accentuates the wave lengths which are preferentially reflected by the surface of the-pigment and consequently the pigment in an enamel,-located as described upon a lightbulb, has an ultimate effect upon the emitted light considerably greater than it would have if such enamel were placed upon a flat screen through which the light was transmitted but once. In such a case, the pigment has but comparatively little coloring effect because its greattest action is in cutting off and turning back a portion of the light.

Because of this repeated reflection of the light across the bulb, there are several somewhat surprising results. One is that a relatively small amount of pigment has a very marked effect upon the color of the light finally emitted, and on the other hand, because of the repeated reflection, the total amount of light emitted from the bulb is reduced very little by even a quite appreciable amount of the pigment. Another is, that the interaction of the pigment and frosting is such that as much as more light is emitted from a given bulb when frosted than when not frosted, while the dispersion of the light is surprisingly increased. I

While the pigment has been described as opaque, and this is the usual condition, it will be understood that distinct colored particles, even if translucent or nearly transparent per se, would nevertheless have an appreciable effect of the same kind because of the reflection at the interfaces between the enamel and particles. Where reflection is referred to in the claims, it is intended to include interfacial reflection. However, to produce the desired results, the reflecting particles are very small.

In one specific construction, about 5 per cent of a modified chrome green enamel is ground with of clear enamel and applied to the bulbs. An analysis of one such specific enamel gave ingredients as follows, calculated as oxides. Parts PbO 8,165 ZnO 1,158 K20 654 C00 23 B203 l 3,820 A1203 47 A5205 40 CraOs 37 Sb203 14 SiOz 1 14,350

-'rio f 1,300

When this enamel is applied to a flat sheet of glass and light passed therethrough, there is some preferential transmission of light in the de- When it is applied to the outside of pigment greatly increases the preferential emission of light in the desired range, and at the same finally transmitted than would be expected from the amount transmitted, without reflection, by a similarly coated sheet of glass.

When the same enamel is applied to an inside frosted bulb; of an electric lamp, the frosting and the pigmented enamel cooperate to reflect and disperse the light so as t decrease surprisingly the maximum brightness, while tests show that the total light emitted from lamps of this kind is at least equal to, and apparently slightly more than, that emitted from lamps otherwise the same but omitting the inside frosting. That is, while inside frosting on bulbs which are not enameled decreases the total light emitted, with the enameled bulbs the frosting does not so decrease the total emitted light, but seems to slightly increase it. Therefore, adding the frosting increases the dispersion, as indicated above, so that it is greater than would be expected from the dispersive powers of the frosting and enamel, taken separately, 1.

and does this without any lessening of the light otherwise emitted from the enameled bulb.

The exact quantitative effect of the enamel depends upon its thickness, the kind and thickness of glass, the source of light, etc., so that exact quantitative measurements of the effects of the enamel on light rays are subject to a considerable range of variation while coming within the scope of the invention, but some measurements will be given by way of example to show the relatively high coloring effect of the enamel on a bulb compared to its effect on a lass plate through which light is transmitted without the benefit of reflection, and also the relatively little loss of the refiected light rays when the effect of reflection is utilized. y

In the following table, the first column gives the light rays in angstrom units, the second, the

per cent of loss for that wave due to enamel on a sheet of glass through which the ray is transmitted without benefit from reflection, and the third column gives the percentage of loss for that ray due to enamel on the exterior of an electric lamp bulb.

Loss on single Loss from t gfi g transmisenameling sion bulb Percent 4, 000 29. 26. 6 4, 500 22. 7 ll. 7 4, 750 20. 5. 5 5, 000 19. 3 4. 6 5, 250 19. 0 3. s 5, 500 19. 0 6 5, 750 20. 3 9. 5 6, 000 20. 3 16 by reflection restores the greater part of this throughout the middle range of visibility, with a rapid dropping off as the ends of the spectrum spectrum with little reduction in those waves most effective in'creating visibility.

This improvement in the quality of the light, coupled with the elimination in glare, results in a light which is both highly efficient and at the same time reducing eye strain to a minimum. As a result, it has been found that when lamps with their bulbs thus enameled are substituted for oth- 'erwise similar lamps without the enamel, ordinary reading may be done with less eye strain and increased visibility is obtained so that better work can be done where acute vision is demanded. For example, in inspection of metal parts, it has been found that flaws were visible under light modified by the enamel, without any increase in electrical consumption, which passed unnoticed under light from the unmodified lamps.

While the pigmentation of the enamel and the thickness of theenamel may be varied, as well as the exact pigmentation of the enamel, it is preferred to employ an enamel that will intercept 20% to 45% of the light that would be otherwise transmitted on single transmission, which results, when employed on the bulb of an electric lamp with tungsten filament, in emission of from to as much total energy in light waves as would be emitted without the enamel. v'I'h'e net result is the emission of light rays between 5000 and 5500 angstrom units in an amount generally 10% to 20% greater in proportion to the total light emitted than would be the case if the enamel were omitted.

Specifically, the chromaticity of the preferred light, in accordance with the 1931 International Commission of Illumination Standard Observer and. Coordinate system is within the area X=438 to 456 and Y=408 to 422. A full description of this system is to be found in Handbook of Colorimetry by Arthur C. Hardy, published by the Technology Press, M. I. T., Cambridge, Massachusetts. See especially Fig. 11 and page 10.

The chromium in the enamel ives a greenish shade, with the cobalt on the blue. side and the antimony on the yellow side. The titanium also affects the chromaticity, but without marked tinting effect.

The light within the range specified does not objectionably tint the objects upon which it falls, and enables the observer to see the colors of objects substantially the same as by daylight. Since the light energy of this light is concentrated largely within the range that affects vision, it is especially valuable for producing properly colored photographs.- In other words, it enables the camera to see objects in the same colors as the eye sees them.

While one composition of enamel is specifically described, it will be understood that various modifications may be made in ingredients and proportions so long as substantially the same selective reflection and consequent modification of light is effected, and while one form of bulb has been shown, it will be understood that any usual orsuitable form of bulb may be employed, the important feature being that portions of the light are reflected repeatedly across the bulb until ultirnately the greater part of the reflected light 7 escapes.

Having thus described the invention, what is claimed is:

approach ultra violet and infra red. This results in reducing wave lengths at the ends of the visible 1. An incandescentelectrlc lamp having a lilainent with the lighting characteristics of a tungsten filament, a glass bulb surrounding the filament and enamel on the'outside of the 01111),

said enamel consisting of a clear base and reflective pigment in an amount to cut off at least 15% and not to exceed 45% of the total light on direct transmission, and sufficiently reflective to result in the ultimate emission of the major part of the light that is cut oiT on single transmission.

2. An incandescent electric lamp having a filament with the lighting characteristics of a tungsten filament, a glass bulb surrounding the filament and enamel on the outside of the bulb, said enamel consisting of a clear base and reflective pigment in an amount to cut ofi at least 15% and not to exceed 45% of the total light on direct transmission, and sufiiciently reflective to result in the ultimate emission of the major part of the light that is cut ofi on single transmission and the pigment being selectively reflective to increase the proportion of reflected light having a wave length of from 5000 to 5500 angstrom units.

3. An incandescent electric lamp having a filament with the lighting characteristics of a tungsten filament, an inside frosted glass bulbsurrounding the filament and enamel on the outside of the bulb, said enamel consisting of a clear base and reflective pigment in an amount to cut oil at least 15% and not to exceed 45% of the total light on direct transmission, and sufiiciently reflective to result in the ultimate emission of the major part of the light that is cut off on single transmission.

4. An incandescent electric lamp having a filament with the lighting characteristics of a tungsten filament, an inside frosted glass bulb surrounding the filament and enamel on the outside of the bulb, said enamel consisting of a clear base and reflective pigment in an amount to cut oil at least 15% and not to exceed 45% of the total light on direct transmission, and sufficiently reflective to result in the ultimate emission of the major part of the light that is cut off on single transmission, and the pigment being selectively re- 6 flective to increase the proportion of reflected light having a Wave length of from 5000 to 5500 angstrom units.

5. An incandescent electric lamp in accordance with claim 1 and the tinting pigment consisting chiefly of compounds of chromium, cobalt and antimony, in an amount, calculated as oxides, constitutin less than 1% of the enamel.

6. An incandescent electric lamp in accordance with claim 1 and the tinting pigment comprising a chromium compound constituting about one eighth of 1% of the enamel composition, calculated as oxides, cobalt and antimony compounds together about equalling the chromium compounds, calculated as oxides, and between four and five per cent of titanium oxide.

7. An incandescent electric lamp in accordance with claim 4 and the enamel having a transmission and reflection color efl'ect substantially equivalent to an enamel of the following composition by analysis, with the base elements calculated as oxides.

Parts PbO 8 ,165 ZnO 1L158 K20 C00 23 B203 4,280 A1203 47 AS205 40 Cr'zOt; 3'7 SbzOs 14: Si02 145350 T102 1,300

8. An incandescent electric lamp in accordance with claim 4, the reflective pigment being of an amount and kind to give the emitted light a chromaticity of X=438 to 456 and Y=408 to 422.

ORMONDE S. LEiVI. RICHARD A. HOYT. 

